1. Field of the Invention
The present invention generally relates to the interconnection of electrical wires, and more particularly to improved wire retention in a modular connector for splicing systems, particularly those used in the interconnection of a plurality of pairs of communications wires. The device includes a main connector body and a wire retention structure which is separably attached to the connector.
2. Description of the Prior Art
There are many prior art systems relating to the interconnection of electrical (copper) wires. One commercially successful modular splicing system used for the interconnection of telephone wire pairs is that described in U.S. Pat. Nos. 3,708,779, 3,713,214, 3,945,705 and 5,030,136, and which is sold by Minnesota Mining and Manufacturing Co. (3M--assignee of the present invention) under the brand name MS.sup.2. The design of one the MS.sup.2 connectors, shown in FIG. 1, is generally rectangular in shape and includes a body bottom portion 1, a body top portion 2, a base or bottom protector 3, and a cover or top protector 4, with a plurality of insulation-displacement, or self-stripping, contact members 5 each having a pair of U-shaped ends for receiving a terminal portion of the wires, and cut-off blades 6 for clipping off the excess portion of the wire ends. Base 3 has a plurality of latches 7 for attachment to body cover 4 has a plurality of similar latches 8. One embodiment is provided with 50 such contacts to allow the simultaneous interconnection of up to 25 pairs of wires. Variations of the MS.sup.2 connector are available for permanent connections as well as bridging or pluggable modules for use in transfers, cutting load coils, and adding relief stubs without interrupting service. Half-tap modules are also available. The cover and base may be clear to allow for visual inspection of the conductors. In addition, the base may be provided with test ports (not shown) to allow for the insertion of probe tips during the splicing operation. The connector may be encapsulated, or formed into preterminated jumper assemblies. See also U.S. Pat. No. 4,093,334 regarding a special base retainer for factory pretermination and testing. The size of the connector and internal elements may vary depending upon the gauge range of the wires to be interconnected. The MS.sup.2 connector is provided in many different variations for different wire size ranges and types of cable construction, i.e., 10 pair and 25 pair binder groups.
The design of the MS.sup.2 connector allows the cover to be removed from the terminated connector body, which enables access to the wires for correction of splicing errors and for maintenance of individual wires within these multiple-pair connectors. Covers must also be removed when plugging additional connector bodies together, in those embodiments which allow vertically plugging of connector bodies, each of which contains one or more sets of terminated wires. While these assembled splice connector designs meet all of the mechanical test standards for the telephone industry, the wires can still become dislodged from their connection points during handling, i.e., when the cover is removed. This is especially true for the largest size wires used in the miniature versions of these connectors. A sorting and splicing station, such as that shown in the '214 patent, may include means for managing the wires during splicing. That splice head provides a spring coil to hold the wires, and individual wire guides aligned with the connector body. This splice head is, however, very bulky and difficult to use during maintenance operations in high-density environments, although stripped-down versions are available to provide minimal support and anchoring. See also U.S. Pat. No. 4,446,617.
Improved strain relief in modular connectors was addressed in U.S. Pat. No. 5,030,136 by the addition of a strain relief feature which is integrally formed with the connector body along an inner portion thereof. This addition, however, results in a wider connector body and more complicated molding tool design. One major obstacle to providing performance improvements to the primary MS.sup.2 design, and to any prior an design, is the requirement of maintaining compatibility to all the previously installed connectors and to the application tooling that comprises the system. A further goal is to be able to utilize existing manufacturing processes for any improved system. Accordingly, the '136 construction does not meet the desiderata relating to compatibility. More specifically, there is not enough space in the existing MS.sup.2 connector footprint to make any feature which would be robust enough to accomplish the wire-holding objective. Any such features would also be very fragile and present difficulties in manufacturing or assembly operations.
The challenge in providing suitable strain relief in miniature, multiple-pair connectors is directly related to the range of wire sizes used in the connector. A feature that holds the smallest wire size will likely experience excessive interference with the largest wire size, making the connector more difficult to splice in those cases. This effect is present in the wire-holding and strain relief geometry of two other prior art designs, those disclosed in U.S. Pat. Nos. 3,611,264, 3,772,635, 3,858,158, 4,262,985 and 4,423,916. Different sizes of certain components, such as the index strip, are necessary with those designs, to accommodate the entire wire size range. An imitation of the MS.sup.2 design, modified by using a wire-holding geometry similar to the "bat-wing" design of the '985 patent, is shown in Brazilian Patent Application No. 8405217, but is generally deemed inferior due to manufacturing and performance disadvantages. The barbed structures discussed in U.S. Pat. Nos. 4,178,055 and 4,836,803 present similar difficulties. Common strain relief designs are likewise not satisfactorily compatible, including those using wire gripping flanges (see U.S. Pat. Nos. 4,127,312, 4,444,449,), those using crimped or deformable sidewalls (see U.S. Pat. Nos. 4,097,106), and those having insulation gripping surfaces (see U.S. Pat. Nos. 4,099,822, 4,236,778, 4,343,529). In all of these designs, the wire retention is integrally formed as part of the connector assembly. There are descriptions of multiple-pair connectors with attachable or separable members providing strain relief, but these generally bundle all the wires together. Thus, these separable members must be removed to gain access to a single wire, exposing all the wires to movement near the contact points; see U.S. Pat. Nos. 4,090,764, 4,488,769, 4,804,342, 4,822,286, 4,840,581, 5,030,111 and 5,158,476. Hinged strain relief members that are held in place over the wires by latches at the ends of the wire array suffer a similar limitation (see U.S. Pat. Nos. 4,538,873 and 4,875,875). Some modular multiple-pair connectors for flat cable have separably attached strain relief members that must be removed to gain access to the wire connections; see U.S. Pat. Nos. 4,538,873 and 5,125,850.
In summary, all of the prior art wire retention and strain relief techniques, when considered in combination with the MS.sup.2 construction, suffer from a wide range of design compromises, performance limitations and manufacturing difficulties. Moreover, none of these designs allow the placement of the wire retention device as an option such that the device is easily added to or separated from the connector body, nor do they provide flexibility in application. It would, therefore, be desirable to devise an improved wire retention and strain relief geometry for securing the wires during cover removal, which overcomes size and compatibility constraints to allow simple hand-held splicing and a mix of wire retention features on a single connector module. It would be further advantageous if the connector design accommodates separably attached wire holding and alignment features on both sides of the connector body without interfering with existing functionality.